It's been baby steps to get here, but today I finally cut my first aluminum parts on my modified 1515 (build here). I'm slotting and putting pilot holes in some 3/4" square aluminum bars. This machine replaced my Shapeoko XXL. I needed the additional cutting area that the 1515 provides. I was concerned about flex & twist on the wide gantry & my modifications were mostly to stiffen the gantry. I cut with a 3/16" single flute HSS bit, at 38IPM - all the same as my Shapeoko. I'm not getting any of the chatter I experienced with the Shapeoko. Right off the bat I was also able to increase my DOC slightly, to .025" from .020". With a little time & testing I think I might be able to do even better, and maybe also increase cutting speed a bit. It's too early to get too excited... I've got about 100 of these bars to cut & we'll see how that goes, but it felt good to get this first aluminum cut under my belt. Thanks to all who have helped me get here!